Cracking the Code: Crucial Blood Tests for Weight Loss Success

Are you feeling frustrated and defeated in your weight loss journey? You’re not alone.

It can be incredibly disheartening when you put in the effort to shed those stubborn pounds, only to see minimal or no results. If you’ve been working on your diet and tirelessly exercising, and still not seeing the number on the scale budge, it’s time to dig deeper.

The truth is that weight loss is not as simple as calories in vs. calories out. There are several factors that could be impacting your metabolism and causing your body to resist weight loss, despite your best efforts. 

In this article, we’ll discuss how the right lab tests can uncover the cause of your weight loss resistance and help you finally start seeing results.

Common Causes of Weight Gain

While your calorie intake is important, excess calorie intake is not the only contributor to weight gain. There are many other factors that can slow down your metabolism and make your body hang on to fat.

Some of the most common causes of weight gain include:

  • Insulin resistance
  • Hormones imbalances
  • Nutrient deficiencies
  • Stress
  • Poor gut health
  • Inflammation
  • Certain medications

When to Consider Lab Testing

Getting some baseline blood work done at the beginning of your weight loss journey can be extremely valuable. Correcting imbalances in your body before you start intentionally trying to lose weight can make weight loss easier. 

I also recommend getting lab work done if you’ve been trying to lose weight for several months with little results, or if you’ve gained weight unexpectedly.

What Blood Tests are Done for Inability to Lose Weight?

The following tests can be done with a simple blood draw. I routinely order these labs for clients in my practice, or you can request them from your primary care physician.

Full Thyroid Panel

Your thyroid gland plays a significant role in regulating your metabolic rate. An underactive thyroid can slow down your metabolism and make it more difficult to lose weight (1).

Most standard lab panels include TSH, which is thyroid stimulating hormone. However, this lab does not provide the full picture of how your thyroid is performing and often misses subclinical hypothyroidism or Hashimoto’s Thyroiditis, which is autoimmune hypothyroidism.

To thoroughly assess the health of your thyroid, you need a full thyroid panel, which includes:

  • TSH
  • Free T3
  • Free T4
  • Reverse T3
  • Anti-TPO antibodies

Vitamin D

Vitamin D, which is actually a hormone, plays an important role in thyroid function, metabolism, and blood sugar regulation. Several studies have found that vitamin D deficiency, which is quite common in the United States, is associated with obesity (2).

I recommend getting your vitamin D level checked at least once a year to ensure optimal levels.


Cortisol is a stress hormone that can cause your body to hang onto body fat, particularly in your abdomen (3). While cortisol is a necessary hormone, excess cortisol or dysregulated cortisol levels can cause weight loss resistance.

While it’s best to measure cortisol at several points throughout the day because it naturally rises and falls throughout a 24 period, a morning cortisol level is a good starting point to look for excess cortisol.

Insulin Resistance Labs

Insulin resistance is the #1 cause of weight loss resistance that I see in my practice. Insulin resistance leads to high insulin levels, which causes the body to store more fat. It also increases appetite and cravings, which often leads to overeating (4).

There are several labs that can be drawn to identify insulin resistance:

  • Fasting glucose
  • HgbA1c
  • Fasting insulin

Fasting insulin is not generally included on a standard lab test, but it’s an important one to include in your labs because it can identify early stages of insulin resistance years before it will be picked up on a fasting glucose (5). I recommend getting all 3 of these labs to assess your blood sugar regulation.

Lipid Panel

Your blood lipids provide information about your cardiovascular health and risk factors, but alterations in these labs can also point to issues with your thyroid or blood sugar management. 

A lipid panel includes:

  • Total cholesterol
  • HDL
  • LDL
  • Triglycerides

Inflammation Markers

Chronic inflammation in the body is another leading cause of weight loss resistance. Chronic inflammation is also a root cause of many health conditions, including cardiovascular disease, cancer, diabetes, autoimmune disease, and Alzehimer’s (6).

The following lab tests of markers of inflammation in the body:

  • hs-CRP
  • Homocysteine

Additional Functional Labs to Consider

While blood tests can be a valuable tool to identify imbalances in the body causing weight loss resistance, sometimes we need to dig a little deeper.

As a Registered Dietitian and Functional Nutritionist, I utilize standard blood work in my practice, but I also use functional tests that go beyond what conventional lab tests can provide.

Function lab tests can look at gut health, hormones, nutrient status, and food sensitivities to identify what’s at the root cause of your health concerns.

Hair Tissue Mineral Analysis

Minerals are the spark plugs of your metabolism. When mineral levels are depleted or out of balance, your metabolism will be sluggish and inefficient.

A hair tissue mineral analysis (HTMA) provides a comprehensive assessment of your mineral status. Your body’s mineral balance provides information about how your thyroid, adrenal glands, digestive system, and more are performing at a cellular level.

This is actually the #1 lab test I recommend for individuals struggling with weight loss resistance.

GI Map Stool Test

The GI Map provides a comprehensive assessment of the health of your gut, and can detect inflammation, bacteria imbalances, and digestive issues.

Inflammation in the gut can lead to widespread inflammation in the body. Certain imbalances in the gut can also significantly impact your metabolism, making it more difficult to lose weight (7).

A functional stool test can provide a snapshot of what’s going in your gut so that I can provide a personalized protocol to rebalance your gut and heal your metabolism.

DUTCH Hormone Test

Hormone imbalances can also make it more difficult to lose weight and signal the body to hang on to excess body fat. Common hormone imbalances I see contributing to weight gain in my practice are cortisol dysregulation and estrogen dominance. 

The DUTCH Complete is a urine test that looks at your hormone levels and how your body is metabolizing hormones. Correcting hormone imbalances with a personalized protocol based on your labs can make weight loss easier.

A Functional Approach to Weight Loss

We have been told for years that weight loss is as simple as calories in vs. calories out. Just eat less and move more, and you’ll lose weight.

If you’ve been trying to lose weight for quite some time and are struggling to see results, you probably already know that it’s not that simple.

A calorie deficit (meaning taking in less calories than your body is burning) is required for weight loss, but so is a healthy, thriving metabolism.

A functional approach to weight loss involves going deeper than just your calorie intake to look at how your metabolism is working. 

As a functional nutritionist, I help you identify why your body is resisting weight loss and help you develop a personalized plan to optimize your metabolism and lose weight in a sustainable way. 

If you feel stuck on your weight loss journey and you’re ready for personalized help, click HERE to book a free 30 minute strategy call with me.

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